(1) Field of the Invention
This invention relates to certain mutant strains of Streptococcus mutans strain BHT-2(str), their mutagenesis and isolation from the parent strain, and their use as an effector strain in the replacement therapy of dental caries.
(2) Description of the Prior Art
Dental clinical investigators have long wrestled with the problem of preventing, or at least alleviating, dental caries, a disease characterized by the dissolution of the mineral portion of the tooth. If permitted to go unchecked, the disease ultimately attacks and penetrates the pulp chamber of the tooth, resulting in pain and loss of viability of the tooth which may necessitate costly repair of the tooth, or even extraction.
A clean tooth will not decay; however, it is also virtually impossible to keep one's teeth continuously clean. And despite the most vigorous cleaning regimen, carious lesions do occur.
Over the years, various methods have been developed and tried, with varying results, to prevent, or at least alleviate, the problem of dental caries. The application of alkali metal or tin flourides to the teeth topically, in drinking water, and in dentifrice preparations containing these flouride compounds which release flouride ions in water is known to be somewhat beneficial. However, it has also been discovered that these compounds tend to lose their effectiveness upon aging. Moreover, flouride reduces caries at best by only about 20% when used in toothpaste.
It has also been proposed to prevent dental caries by coating the tooth surfaces with various polymeric materials. However, at least one of these proposals suffers from at least two drawbacks. The teeth must first be etched with phosphoric acid; and, the treatment has been found to be effective only in young children who have not yet developed dental caries.
The formation of carious lesions in teeth, it has been observed, is apparently caused by acids produced by bacteria, e.g. the interaction between carbohydrates, notably sucrose, and bacteria on the tooth surfaces, as an end product of their metabolism. A variety of specific organisms have been described as etiologic agents of dental caries, notable among which are bacteria of the genus Streptococcus. Various Streptococci have been isolated from the oral cavity and have been linked to the formation of dental caries in experimental animals.
Antibiotics such as penicillin have been suggested for reducing caries, and dentifrices containing penicillin have been tested and found to be effective. However, the antibiotics are not selective in the destruction of oral bacteria and destroy both the useful and harmful bacteria in the mouth indescriminately, resulting in microbial imbalance in the mouth which can have serious consequences.
A number of vaccines have been proposed for immunization against dental caries in animals. Various of these proposals are summarized in U.S. Pat. No. 3,879,545 issued to Gaffar and Kestenbaum for "Vaccines for the Prevention of Dental Caries", issued on Apr. 22, 1972. As disclosed therein, the active ingredient of the vaccine is a polyfructan (or levan) polysaccharide produced by elaboration of certain strains of Streptococcus, particularly Streptococcus strain SS2.
There are also disclosed in U.S. Pat. Nos. 3,931,398 and 3,993,747, methods of immunization against dental caries employing as the active ingredient the polysaccharide of U.S. Pat. No. 3,879,545, or the polyglucan elaboration product described therein from Streptococcus mutans, or the enzyme involved in the synthesis of these polysaccharides selected from among levansucrase (fructosyl transferase) and dextransucrase (glucosyl transferase).
A large body of evidence has implicated Streptococcus mutans as a principal pathogen in dental caries of both rodents and humans. Fitzgerald, R. J. and P. H. Keyes. 1960. Demonstration of the Etiologic Role of Streptococci in Experimental Caries in the Hamster. J. Am. Dent. Ass. 61: 9-13; Gibbons, R. J., K. S. Berman, K. S. Knoetter, and B. Kapsimalis. 1966. Dental Caries and Alveolar Bone Loss in Gnotobiotic Rats Infected With Capsule Forming Streptococci of Human Origin. Archs. oral Biol. 11: 549-559; Krasse, B. 1966. Human Streptococci and Experimental Caries in Hamsters. Archs. oral Biol. 11: 429-436; and Zinner, D. D., J. M. Jablon, A. P. Aron, and M. S. Saslaw. 1965. Experimental Caries Induced in Animals by Streptococci of Human Origin. Proc. Soc. Exp. Biol. 11: 429-436; deStoppelaar, J. D., J. van Houte, and O. Backer Dirks. 1969. The Relationship Between Extracellular Polysaccharide Producing Streptococci and Smooth Surface Caries in 13-year-old Children. Caries Res. 3: 190-199; Krasse, B., H. V. Jordan, S. Edwardsson, I. Svensson, and L. Trell. 1968. The Occurrence of Certain "Caries Inducing" Streptococci in Human Dental Plaque Material. Archs. oral Biol. 13: 911-918; and Littleton, N. W., S. Kakehashi, and R. J. Fitzgerald. 1970. Recovery of Specific "Caries-Inducing" Streptococci From Carious Lesions in The Teeth of Children. Archs. oral Biol. 15: 461-463.
The characteristic features of Streptococcus mutans which appear likely to account for its cariogenic potential include not only its ability to accumulate on tooth enamel, but also its ability to produce, via fermentative processes, large amounts of lactic acid. Gibbons, R. J. and R. J. Fitzgerald. 1969. Dextran-induced agglutination of Streptococcus mutans and its potential role in the formation of microbial dental plaques. J. Bacteriol. 98: 341-346; Makinen, K. K. 1972. The role of sucrose and other sugars in the development of dental caries: a review. Int. Dent. J. 22: 362-386; Drucker, D. B. and T. H. Melville. 1968. Fermentation end-products of cariogenic and non-cariogenic Streptococci. Archs. oral Biol. 13: 563-570; Jordan, H. V. 1965. Bacteriological aspects of experimental dental caries. Ann. N.Y. Acad. Sci. 131: 905-912; and Tanzer, J. M., M. I. Krichevsky, and P. H. Keyes. 1969. The metabolic fate of glucose catabolized by a washed stationary phase caries-conducive Streptococcus. Caries Res. 3: 167-177.
In recent years, considerable success has been achieved in preventing and controlling certain bacterial infections by purposefully colonizing susceptible host tissues with non-virulent analogs of disease-causing microorganisms. Davidson, J. N. and D. C. Hirsh. 1976. Bacterial Competition as a Means of Preventing Neonatal Diarrhea in Pigs. Infect. Immun. 13: 1773-1774; Shinefield, H. R., J. C. Ribble, and M. Boris. 1971. Bacterial Interference Between Strains of Staphylococcus aureus, 1960-1970. Amer. J. Dis. Child. 121: 148-152. The basis of this phenomenon, termed bacterial interference, is in no single case completely understood, but in general terms appears to involve a competitive and/or antibiotic action of the non-virulent strain, the so-called effector strain, on its pathogenic counterpart. Thus, for an organism to serve as an effector strain in the replacement therapy of a bacterial infection, it must be (a) non-virulent itself, and (b) able to compete successfully with its pathogenic counterpart.